wireless: Only join DFS channels in mesh mode if userspace flags support

When joining a mesh network it is not guaranteed that userspace has a
daemon listening for radar events. This is however required for channels
requiring DFS. To flag that userspace will handle radar events, it needs
to set NL80211_ATTR_HANDLE_DFS.

This matches the current mechanism used for IBSS mode.

Signed-off-by: Benjamin Berg <benjamin@sipsolutions.net>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/wireless/mesh.c b/net/wireless/mesh.c
index ec0b1c2..421a6b8 100644
--- a/net/wireless/mesh.c
+++ b/net/wireless/mesh.c
@@ -174,6 +174,14 @@ int __cfg80211_join_mesh(struct cfg80211_registered_device *rdev,
 							       scan_width);
 	}
 
+	err = cfg80211_chandef_dfs_required(&rdev->wiphy,
+					    &setup->chandef,
+					    NL80211_IFTYPE_MESH_POINT);
+	if (err < 0)
+		return err;
+	if (err > 0 && !setup->userspace_handles_dfs)
+		return -EINVAL;
+
 	if (!cfg80211_reg_can_beacon(&rdev->wiphy, &setup->chandef,
 				     NL80211_IFTYPE_MESH_POINT))
 		return -EINVAL;